Method of making a gas phase permeable filter

ABSTRACT

Described is a gas phase permeable filter and method for making same comprising the steps: 
     1. providing a gas phase permeable substrate having opposite surfaces; 
     2. applying an adhesive to one or both of the surfaces of the substrate; 
     3. applying particulate gas phase odor-removing means to the adhesive coated surface or surfaces of the substrate; 
     4. drying the adhesive; and 
     5. assembling the substrate in a desired filter configuration wherein the outer surface of the filter is a surface of the substrate free of particulate gas phase odor-removing means and the inner surface of the filter is a surface of the substrate coated with the particulate gas phase odor-removing means adhesively secured thereto.

This application is a continuation of application Ser. No. 135,186,filed Mar. 28, 1980 now abandoned, which was a division of Ser. No.940,721, filed 8, Sept. 1978, now U.S. Pat. No. 4,227,904, which was acontinuation of application Ser. No. 709,665, filed 29, July 1976, nowabandoned.

BACKGROUND

Various gas phase filters have been described in the patent literature.U.S. Pat. No. 3,645,072 shows a granular activated carbon filter withina frame of U-shaped channels. The bonded activated carbon body may bereinforced with a wire or other network. U.S. Pat. No. 3,630,007 teachesa disposable activated charcoal filter having a frame open at both sidesand subdivided into a plurality of compartments by intersectingpartitions. U.S. Pat. No. 3,350,860 teaches granular activated carbonpoured into filter containers. U.S. Pat. No. 3,474,600 teaches activatedcarbon particles bonded together by monoolefin polymers to form pelletsand the pellets are then bonded to each other by the polymer to formlarger shapes. U.S. Pat. No. 2,544,733 teaches a filter for removingodorous qualities from gasses containing a rigid outer frame and anmultiplicity of spaced flexible webs carried within said frame and aplurality of layers of granular odor-adsorbing material carried betweenand substantially filling the spaces between said webs. The granules ofodor-absorbing material being adhesively united to adjacent surfaces ofsaid webs by means of tapes to prevent relative displacement of saidgranules with respect to said webs. U.S. Pat. No. 3,577,710 teachesreactant pellets placed in a honeycomb sheet structure and retainedtherein by foam rubber or plastic cover sheets. U.S. Pat. No. 3,870,495teaches non woven laid fibers used in air filters. U.S. Pat. No.3,721,072 teaches a filter for removing odors comprised of granulesbonded together in a monolithic extended surface shaped in the form of awave. U.S. Pat. No. 3,873,287 teaches the construction of assemblies ofgranular material filled adsorbers or filters for fluids using modularcomponents readily standardized to facilitate assembly of a variety offilter unit sizes and in diverse patterns from stock manufactured parts.

SUMMARY OF THE INVENTION

It is an object of the present invention to manufacture gas phasepermeable filters of what may be conveniently referred to as the "thinbed" type by a quick and convenient method, specifically adhesivelysecuring particulate gas phase odor-removing means to a substrate orgrid.

Also described in a gas permeable filter comprising:

a gas phase permeable substrate; and

particulate gas phase odor-removing means adhesively secured to the gasphase permeable substrate.

The gas phase filter, in particular an air filter, obtained by theprocess of the present invention is one that is lightweight, has littledrop in pressure in the flow of air therethrough, is efficient in theremoval of odorous qualities from the gas phase, and substantiallyreduces or eliminates loss from the filter of the material comprisingthe particulate odor-removing means. In addition, the improvedconstruction prevents settling of the odor-removing means within thefilter both prior to and during use of the filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of the thin bed gas phase filter of the presentinvention in a final assembled condition;

FIG. 2 is a schematic drawing showing the manufacture of the filter ofFIG. 1;

FIG. 3 is a cut away of the filter of FIG. 1;

FIG. 4 is a filter of the present invention having a backing of agrease, dust and smoke and other particulate removal means such as aglass fiber batt;

FIG. 5 shows a filter obtained by use of a single grid or substrate thathas been spirally wound or rolled to a desired shaped with particulategas phase odor-removing means adhered to both faces of the substrate;

FIG. 6 is cross-sectional view taken on the line 6--6 of FIG. 5;

FIG. 7 shows a filter similar to FIG. 1 except one substrate is a fiberglass batt or the like;

FIG. 8 is another embodiment of the present invention wherein the gridor substrate of the filter is a laminate such as paper and metal;

FIG. 8A is another embodiment of the present invention wherein the gridor substrate of the filter is a laminate comprising a paper laminacovered on both sides by aluminum foil laminae;

FIG. 9 is a fragmentary cross-sectional perspective similar to FIG. 1but shows an intermediate grid between the two outer sheets withparticulate gas phase odor-removing means adhesively secured to oppositefaces thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

The gas phase permeable thin bed filter such as the thin bed air filtershown herein is manufactured by the following steps:

1. providing a gas phase permeable substrate having opposite surfaces;

2. applying an adhesive to one or both surfaces of the substrate;

3. applying particulate gas phase odor-removing means to the adhesivelycoated faces of the substrate;

4. drying the adhesive; and

5. assembling the substrate in a desired filter configuration whereinthe inner surface of the filter is a surface of the substrate coatedwith the particulate gas phase odor-removing means and the outer surfaceof the filter is a surface of the substrate uncoated with theparticulate means.

There are numerous applications in the home, such as ductless rangehoods, room air purifiers, electronic air cleaners, air conditioners,and heating, ventilating systems. Normally the odors to be removed arethose generated by human activities and include cooking and smoking, orodors from pets or other animals, or human waste.

In addition, there may be more stringent filtering requirements such ascommercial/industrial applications, where fuel exhaust (airports orpower plants) and/or manufacturing operations generate specific, and inmany cases concentrated odorants which may not only be objectionable,but may be also toxic, i.e., sulfur dioxide, formaldehyde, phenols, andthe like. In order to remove specific odors, appropriately designed,impregnated, or selected gas phase odor-removing means may be employed,with or without the use of a means for removing smoke, dust, or otherparticulates.

The gas phase odor-removing means may be any particulate substance, suchas flakes, particles, pellets or granules. Generally the particles havea range in size from 12/28 to 4/6, preferably 6/8 mesh measured byeither U.S. or Tyler screen series. The filtering means itself, that isthe gas phase odor-removing means, may be activated carbon, having apelletilized, flake, or granulated size and shape, and may be obtainedfrom a supplier such as Union Carbide Corporation, or it may be Purafil(Trademark of H. E. Burroughs and Associates for potassium permanganateimpregnated activated alumina), or it may be Sanilan (Trademark of ColloG.M.b.H. of West Germany for a chemisorptive filter medium in pellitizedform.) These particulate materials may be impregnated with appropriatecounteracting materials to the odor-producing substances present in thegas phase which one wishes to purify. For example, there may be anappropriate impregnant in activated carbon, for example to combat thesulfur dioxide, formaldehyde or phenol substances present in the gasphase that one wishes to purify.

The grid or substrate that is used in the present application can bemade of a variety of substances. It may be made of appropriate metallicelements such as aluminum, or tin-plated cold-rolled steel, a laminateof paper or paper and metal such as aluminum foil, or a paper substanceupon which has been sprayed or applied a reinforcing or strong-adheringcoating such as a metallic backing. All that is required for thesubstrate is that it have appropriate porosity and be stable in theenvironment in which the filter is used. The substrate should be capableof allowing the gas phase to be filtered to pass freely therethrough. Inthe case of sheet-like substrates the sheets may be perforated to havean open area as low as 20 percent and a high of about 65 percent,preferably about 45 percent. This should be accomplished by having asubstrate having holes of a diameter less than the size of theparticulate media. The substrate shown in a preferred embodiment mayrange from 0.012"-0.040" in thickness.

The adhesive that may be applied to the substrate prior to theapplication of the particulate gas phase odor-adsorbing substance toadhere the same to the substrate would be any adhesive which couldconveniently and securely bond the filtering particles to the substrate.The adhesive must be a strong adhesive and must be one that does notsubstantially surround the filtering particles itself because theadhesive may then decrease substantially the effectiveness of thefiltering medium such as the activated charcoal. In addition, theadhesive must be stable in the environment of the medium in which thefilter is used as well as retain its adhering properties to retainsecurely the particles thereto. Preferably, the adhesive is one that maybe tackified by the application of heat to increase the drying of theadhesive.

The most preferred adhesive is one sold by 3M and identified aslaminating adhesive XB-4236 which is a water dispersion containing 47percent solids content and is a soft gel primarily polychloroprene-basedsubstance weighing about 9.1 pounds per gallon and having a viscosity ofapproximately 3,000 cps.

The adhesive must be applied to the substrate in such manner as to avoidunwanted seepage through the holes to the opposite face of thesubstrate. Preferably, it is roll coated onto the substrate to ensureuniform application thereto of approximately 1 mil thickness. Theadhesive must be capable of withstanding the appropriate temperatures ofthe gas phase application such as being stable up to approximately 300°F. The adhesive is one that should be capable of drying in a relativelyshort period of time. Additionally, the adhesive should be applied suchthat it does not fill the holes in the substrate thereby decreasing itsporosity.

Turning now to a discussion of the drawings, FIGS. 1 and 3 shows filter10 of the present invention having a pair of spaced apart perforatedgrids 11 and 12 each having holes 13 therethrough retained in a U-shapedchannel frame 14. The frame may comprise a single U-shaped channel bentat the four corners and locked at the meeting ends by locking tab 16,conventional in a filter frame construction. Between the grids 11 and 12and holding them in spaced apart relation as shown in FIG. 3 isparticulate gas phase odor-removing means 35.

The thin bed filter 10 is manufactured according to FIG. 2. Roll stock18 in the form of a self-supporting perforated substrate having a widthcorresponding to the width of the filters to be formed, is fed to acutter 20. The substrate cut to successive lengths correspinding to thelength of the filters to be formed is passed onto a continuous belt 22maintained between rolls 24 and 26. Adhesive from reservoir 28 isapplied by roll coater 30 to the cut grid. A drying oven 32 is stationedabove the adhesively treated grid 18a and tackifies the adhesive bysubjecting the grid to tackifying temperatures such as 160° F.Thereafter, and before the adhesive hardens, a uniform layer of gasphase removing particles 35 are deposited from tank 34 onto thetackified grid. Because the adhesive dries very quickly the grid withthe adhesively secured particles may be handled at the end of thecontinuous belt at station 36. Desirably, following removal of thesubstrate at station 36, it is inverted and shaken to remove excess,non-adhered particles. The filter 10 of FIG. 1 is obtained by assemblingtwo grids from station 36 by placing one on top of the other with theinner surfaces of the grids facing each other as shown at 38. The twogrids are then assembled in the U-shaped frame 14 as best shown in FIG.3.

It is important that the adhesive be sufficiently tackified by the oven32 that when the particulate material is deposited thereon at 34, theadhesive will not appreciably capilate into the particulate material andmaterially reduce its effectiveness. At the same time the adhesive mustnot have so far set up as to prevent the particulate material fromsettling into it in bonding contact therewith.

With the grids assembled as shown in FIG. 3 (and also FIG. 4) thegranules or pellets 35 adhered to the grids are disposed in abuttingcontact. The entire surface areas of the particulate material except forthe small areas in contact with the adhesive on the grids are free toadsorb the odors from the gas phase passed through the filter. Theabutting contact of the particles 35 serves to space the substrates 11and 12 apart.

The U-shaped frame may be manufactured from appropriately shapedmetallic or may be lightweight plastic such as polyvinyl chloride orother plastics which are not suseptible to corrosion in the environmentin which the filter will be used.

In a modified form of the FIGS. 1 and 3 filter, a batt of loosely mattedglass fibers 40 or other suitable non-woven material may overlie theouter face of grid 11 as shown in FIG. 4. The glass fiber batt willenhance the grease, dust, smoke and other particulate removal capabilityof the filter. It is held in place against substrate 11 by adhesivebonding thereto. The adhesive is preferably applied to the substrate andbefore drying the batt is juxtaposed thereagainst. The channel frame 14overlies the edges of the batt further retaining same against thesubstrate.

In FIGS. 5 and 6 a filter of cylindrical shape is shown. It is formed byspirally winding a perforated substrate coated on one but preferablyboth sides with a uniform layer of particulate odor-adsorbing medium 44.The substrate with the adsorbing particles is spirally wound upon itselfto form a hollow central tube 59 into which air or other gas to befiltered is introduced at a central gas entering aperture 60. The gasthen passes radially outwardly as indicated by the arrows in FIG. 6. Aclosure cap 62 overlies one end of the filter and an annular cap 64overlies the opposite end and defines the central gas entering aperture.

In constructing the filter of FIGS. 5 and 6 a length of perforatedsubstrate 66, such as a flexible laminate of paper having aluminum foilbonded to opposite faces, is coated with an adhesive on both faces andthe odor-removing means is then uniformly deposited on the coated faces.End portions of the substrate which when wound into the spiral shapewill define the exposed wall 65 of the central tube 59, as well as theouter surface 68 of the filter, are left uncoated so that the aluminumfoil surface is exposed. Also, if desired, the aluminum foil may coveronly those surfaces of the substrate which will be exposed as aforesaid,the remaining surfaces of the substrate being the paper itself with theparticulate odor-adsorbing media bonded thereto. Where the inner andouter ends 70 and 72 of the spiral wrap lap adjacent convolutions, theends may be adhesively secured or stapled thereto.

Alternatively, if desired, a length of perforated paper substrate may becoated on both faces and the odor-adsorbing media adhered thereto andthen the paper wound into spiral form. Over the outside a tube formed ofa perforated substrate of paper and aluminum foil having theodor-adsorbing media bonded to the inside of the tube and the foilexposed on the outside may be slipped over the spiral form. A similarbut smaller tube with the foil on the inside and media bonded to theoutside may be inserted into the center of the spiral, and the hole thenclosed at opposite ends with caps similar to 62 and 64.

The construction of FIGS. 5 and 6 represent a substantial improvementover the prior art wherein a filter formed by concentric tubes havingend caps similar to 62 and 64 is simply filled with loose carbonparticulate or similar material because the weight is reduced, air flowimproved, the odor-adsorbing media will not settle, and the filter willnot bleed carbon fines through the holes.

A further modification of the filter of FIGS. 1 and 3 is shown in FIG. 7wherein the grid 11 is omitted and in its place a glass fiber or similarbatt 72 is substituted. The grid 12, with adhesively bondedodor-adsorbing particles 35, is manufactured as above described. Thebatt 72 has one surface sprayed or otherwise applied with adhesive andthen such surface, following tackification, is juxtaposed against theodor-adsorbing particles 35. Upon curing of the adhesive the batt isretained in place.

The grids or substrates above mentioned may be all metal, or may be alaminate of a cellulosic material such as paper 52 and metal 54 such asaluminum foil as shown in FIG. 8. This substrate may be processed byapplying adhesive 42 to the paper surface and particles 35 thendeposited thereon. A filter resulting from the substrate adhesivelysecured particles of FIG. 8 is extremely lightweight and the metal foilacts to strengthen the laminate and protect the paper and as areflective insulator and provide a decorative finish. The adhesive isroll-coated to the paper side of the substrate and the odor-removingparticles 35 applied thereto as above described. The aluminum foil may,if desired, be on both faces of the paper sheet as shown in FIG. 8A,where aluminum foil laminae 54' and 55 overlie opposite sides of thepaper lamina 52' and the odor-adsorbing particles 35' are adhered to theexposed face of the foil lamina 55. However, it has been found that theadhesive applied by roll coating will tend to be adsorbed to some extentby the paper and act as a protective layer thereon obviating the use offoil on the inside surface of the filter.

In FIG. 9 a filter is shown which includes three grids 80, 82 and 84.Grids 80 and 84 are similar to grids 11 and 12 of FIGS. 1 and 3. Grid 82may comprise either a perforated metal or paper or paper/aluminum foillaminate, on opposite faces of which is adhesively fixed uniform layers86 and 88 of particulate odor-adsorbing media. The grid 82 with oppositefaces exhibiting the particulate media is sandwiched between the grids80 and 84 and the composite enclosed in a frame 90 similar to the FIGS.1 and 3 structure. This construction substantially doubles theefficiency and life of the filter as compared with the construction ofFIGS. 1 and 3.

What is claimed is:
 1. The method of making an odor removing thin bedfilter comprising the steps:(1) providing a self supporting perforatedsheet-like substrate having opposite faces and discrete perforationsextending through the substrate and opening through the faces with thesubstrate having a width substantially equal to the width of the filtersto be formed and a length sufficient to form several filters; (2)cutting such substrate into successive equal lengths, each substantiallyequal to the length of each filter to be formed; (3) depositing the cutlengths successively on a moving conveyor belt with one face disposedupwardly and the other lying on the belt to transport the cut lengthsthrough a series of work performing stations; (4) at a first station,roll-coating the upwardly disposed face of each of the successivelengths of substrate with an adhesive without seepage of the adhesivethrough the perforations to the other face; (5) at a second station,tackifying the adhesive coating sufficiently to prevent any appreciablecapillation into the odor removing particles to be subsequently applied;(6) at a third station and before the adhesive hardens preventing odorremoving particles from settling into it, applying a uniform layer ofsuch particles ranging in size from approximately 12/28 to 4/6 measuredby the Tyler screen series to the upwardly disposed face of thesubstrate on top of the tackified adhesive coating with the particlessettling into the coating; (7) while continuing to transport the cutlengths on the conveyor, curing the adhesive to a condition retainingthe particles; (8) removing the successive lengths of coated substratesfrom the conveyor and removing unadhered particles therefrom; (9)assembling two such coated substrates with the coated faces in opposingabutting contact; and (10) securing a peripheral frame around and to thethus assembled pair of substrates to integrate them into a filterstructure.
 2. The invention defined by claim 1 wherein the unadheredparticles are removed by inverting the cut lengths to dispose the coatedface downwardly.